The present disclosure generally relates to methods for additive manufacturing that utilize supports in the process of building an object, as well as novel self-breaking supports to be used within these AM processes.
Additive manufacturing (AM) processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term, AM encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. AM techniques are capable of fabricating complex objects from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer aided design (CAD) model. A particular type of AM process uses an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a metal powder material, creating a solid three-dimensional object in which particles of the powder material are bonded together. Different material systems, for example, engineering plastics, thermoplastic elastomers, metals, and ceramics are in use. Laser sintering or melting is a notable AM process for rapid fabrication of functional objects, prototypes and tools.
Selective laser sintering, direct laser sintering, selective laser melting, and direct laser melting are common industry terms used to refer to produce three-dimensional (3D) objects by using a laser beam to sinter or melt a fine metal powder. These processes may be referred to herein as metal powder additive manufacturing. More accurately, sintering entails fusing (agglomerating) particles of a powder at a temperature below the melting point of the powder material, whereas melting entails fully melting particles of a powder to form a solid homogeneous mass. The physical processes associated with laser sintering or laser melting include heat transfer to a powder material and then either sintering or melting the metal powder material.
Metal powder additive manufacturing processes create layers of molten metal or an agglomeration of metal over already formed layers of hardened metal. Where the hardened metal is under the new layer, the hardened metal supports the new layer. One challenge of additive manufacturing is building surfaces that are not vertical such as unsupported horizontal surfaces or vertically angled surfaces, i.e., those angled relative to horizontal with no support therebelow. More specifically, where a portion of the new layer is not over a previously formed, now hardened metal, the non-heated metal powder thereabout provides insufficient support and gravity negatively impacts the object's final shape. In order to address this situation, during metal powder additive manufacture of a metallic object, it is known to also form supports as part of the metallic object to support the otherwise unsupported surfaces. For example, supports may be formed in fuel nozzles, such as those used in gas turbines, to maintain separation between parts, e.g., spaced, concentric tubular components in close proximity to one another. In many applications, the supports are removed from the final metallic object, e.g., where operation using the object does not allow for the presence of the supports or support breakage may cause other damage. In these situations, the supports are removed through post-AM processes such as machining or chemical processes. In some cases, supports built into the metallic object are allowed to remain in the object. In this case, stresses, such as thermal stress observed during operation of the metallic object, may be allowed to break the supports. The breakage may be allowed, for example, to improve operation by allowing for more freedom of movement during stresses observed within the object. It is difficult, in some applications, to ensure that the supports are configured to break during operation in a manner that does not otherwise impact the object. Another challenge is supporting surfaces where other structure in the surfaces, such as fluid passage openings, are present. In these instances, supports cannot be used because they interfere with the other structures. While these challenges have been described relative to metal powder additive manufacturing, they are also present in other forms of additive manufacturing.